Fuse construction



Oct. 6, 1964 F. J. SCHULTZ FUSE CONSTRUCTION Filed June 16, 1961INVENTOR. Fred J Schultz United States Patent 3,152,236 FUSECONSTRUCTION Fred J. Schultz, Miiwaukee, Wis, assignor to McGraw- EdisonCompany, Milwaukee, Wis, a corporation of Delaware Filed June 16, 1961,Ser. No. 117,744 3 Claims. (Cl. 200-427) This invention relates tocircuit interrupting devices and more particularly to an improved fuseconstruction for a fuse cutout of the expulsion type.

Conventional fuse cutouts utilize a fuse construction which includes afuse link, a gas evolving fusetube and a fuse link tube which ispositioned within the fusetube in surrounding relation to a portion ofthe fuse link. Due to the large ranges of currents'(l004000 amperes)which must be interrupted by present day fuse cutouts a conflict in thedesign of the fusetube arises. While it is desired to provide a shortare path in a relatively large bore tube for interruption of highcurrents, it is on the other hand desirable to provide a long are pathin a restricted tube bore for interruption of lower currents. Thissituation is somewhat resolved thru the use of the fuse link tube, inthat low fault currents are interrupted within the confines of the fuselink tube while higher fault currents cause the tube to rupture and arethereby interrupted in the larger fuse tube bore. The success of thisscheme is however relatively limited and does not provide for enlargingthe bore of the larger tube in order to extend the interrupting ratingof the device upward. This then is one of the major disadvantagesinherent in contemporary devices.

It is therefore an object of this invention to provide an improved fuseconstruction for an expulsion type fuse cutout.

Another object of this invention is to provide a fuse constructionhaving improved current interrupting capabilities.

Another object of this invention is to provide a fuse constructionwherein the bore of the main fuse tub is partially relieved of lowcurrent interruption.

A further object of this invention is to provide a fuse construction inwhich the length of high current arcs is materially reduced.

A further object of the invention is to provide a fuse constructionwhich is capable of successfully interrupting a wide range of currents.

A still further object of this invention is to provide an improved fuseconstruction for an expulsion type fuse cutout which is economical toproduce, dependable in operation and which at the same time achieves allthe foregoing advantages.

Other objects and advantages of my invention will be apparent from thefollowing description of the preferred embodiment of the invention takenin connection with the accompanying drawings in which:

FIGURE 1 is a view in elevation of a fuse cutout incorporating theinvention disclosed herein; and

FIGURE 2 is a cutaway portion of a view in elevation of the invention.

Referring to FIG. 1, indicates one form of fuse cutout with which theinvention may be utilized. The cutout 10 comprises an insulator 11 whichmay be made of porcelain or similar insulating material and which isaflixed to a supporting member by means of a hanger bracket assembly,neither of which are shown for the sake of convenience. An upperstationary contact assembly 12 and a lower stationary contact andsupporting structure 13 are fixedly attached to insulator means 11 atspaced apart locations thereon. A fuseholder assembly comprising afuseholder 14, fuse link 15 positioned therewithin and extending out oneend of the holder 14, and

Patented Oct. 6, 1964 "ice upper and lower fuseholder contacts 16 and 17respectively, is pivotally mounted in support 13 and adapted toreleasably engage the upper stationary contact assembly 12 thru areleasable latch construction which is not shown for the sake ofconvenience and to shorten the disclosure. The end of the fuse linkextending out of the fuseholder 14 is aflixed as is customary to thelower contact assembly.

As is conventional, upon a fault within the rating of the cutout, thefuse link will rupture and the fuseholder and its associated contactswill pivot about the support 13 thereby providing visual indication ofthe condition of the line and cutout as well as insuring a safety airgap. To put the cutout back into service a new fuse is inserted in thefuseholder and the fuseholder is rotated back into circuit bridgingposition Where it is maintained by the latch.

Referring now to FIGURE 2, 14 again designates the fuseholder generally.The fuseholder comprises a gas evolving fuse tube 18 which may be madeof melamine impregnated fiber glass or similar materials which are wellknown in the art.

Afiixed to one end of the fuse tube 18 as by screw threads 19 is anapertured ferrule member 20 which may have an inwardly extending uppershoulder portion 21. A fuse assembly comprising a fuse link leader 22,fusible element 23 and button head 24- is positioned within the fusetube 18 so that the underside of the button head 24 contacts theinwardly extending shoulder portion 21 of ferrule member 20. A capmember 25 which may or may not be pressure responsive is affixed to theferrule member 20 by means of screw threads 26. A gas evolv ing fuselink tube 27 which may be made of fiber or similar material ispositioned around the fusible element 23 and a portion of the fuse linkleader 22 and contacts the underside of the button head 24.

Up to this point a conventional fuseholder assembly has been describedand as a result the assembly may take a variety of forms. Therefore theparticular fuse tubes, ferrule members, fuse links and fuse link tubesutilized should not be construed as a limitation on the inventiondescribed herein.

Positioned within the fusetube 18 and surrounding the fuse link tube 27is a tubular conducting member 28 which may be of metal such as brass orsteel or which may take the form of a cylindrical metallic screen. Thebore of the conducting member 28 may vary between the outside diameterof the fuse link tube and the inside diameter of the fuse tube. However,to accomplish the desired results the bore of the conducting tube shouldbe such that it fits snugly around the outside of the fuse link tube 27.By the same token, for best results, the length of the conducting membershould be somewhat less than the length of the fuse link tube 27 Thefunction of the tubular conducting member will now be explained. On verylow fault currents the fusible element 23 is ruptured and an arc isdrawn between the ruptured ends of the element within the confines ofthe fuse link tube. Since the bore of the fuse link tube 27 is exposedto this are gases are evolved from the tube. The gases so evolved,acting in the small space within the fuse link tube, serve to extinguishthe are. The tubular conducting member 28 serves to reinforce the fuselink tube 27 in the area surrounding the fusible element 23 and thuslyincreases the current level at which the fuse link tube will rupture.Therefore higher currents may be interrupted prior to rupture of thefuse link tube than have heretofore been possible. Consequently thevalues of minimum current to be interrupted in the main bore of the fusetube are increased. As a result the diameter of the main fuse tube boremay be materially increased so as to more efiiciently interrupt thehigher values of current without at the same time diminishing thelowcurrent clearing ability of the device.

On higher currents the fuse link tube 27 will rupture in that area belowthe tubular conducting member. Subsequent to rupture, as a result of theheat of the are, gases will be evolved from the fuse tube to extinguishthe are. To limit the internal pressures due to the high current arereacting with the gas evolving material of the main fuse tube, the lowerterminus of the tubular conducting member serves as a terminus for theare thus decreasing the overall length of the are.

It can therefore be seen that the incorporation of the tubularconducting member serves to aid in providing the most optimum conditionsfor both high and low current interruption. Thru the use of the tubularconducting member on low current operation a relatively long are isdrawn in a relatively confined space; the are being extinguished bygases evolved from the fuse link tube. On higher current operation thecurrent are is exposed to the larger bored fuse tube and the arc itselfis shortened as a result of current passage thru the conducting member.

Basically tr en my invention serves to increase the overall currentinterruption of a conventional fuse cutout thru a simple inexpensiveexpedient which has none of the drawbacks associated with similarattempts at upgrading the ratings of cutouts.

While one particular embodiment of the invention has been shown anddescribed, it will be obvious to those skilled in the art that variouschanges and modifications can be made therefrom without departing fromthe invention and, therefore it is intended for the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

I claim:

1. In a fuse cutout of the expulsion type, in combination, a gasevolving expulsion fuse tube, upper and lower metallic contacts adjacentthe ends of said fuse tube, a fuse link including a fusible elementextending axially through said fuse tube, said fuse link including abutton head electrically connected to said upper contact and a dependingcylindrical shank and being connected adjacent its lower end to saidlower contact, an insulating tube of gas evolving material surroundingsaid fusible element and said depending shank within said fuse tube, aconductive sleeve within said fuse tube closely adjacent said insulatingtube along the entire length of said fusible element and having anexternal diameter substantially smaller than the inner diameter of saidfuse tube, said fuse link, said insulating tube, and said conductivesleeve being stationarily mounted relative to said fuse tube, saidinsulating tube being rupturable as a result of current flow throughsaid fuse link and said conductive sleeve structurally reinforcing saidinsulating tube and thereby increasing the magnitude of current that canbe extinguished in said insulating tube without rupture thereof, thelower end of said insulating tube extending beyond said sleeve and highmagnitudes of current flowing through said fuse link rupturing saidinsulating tube, the gases evolved from said expulsion fuse tube as theresult of the are formed by said higher magnitudes of currentextinguishing said are, said conductive sleeve serving as the -5-terminus for said are and reducing the length of the are within saidfuse tube, whereby the internal pressure within said fuse tube isdecreased.

2. In a fuse cutout of the expulsion type, in combination, a gasevolving expulsion fuse tube, a metallic contact adjacent one end ofsaid fuse tube, a fuse link electrically connected to said contct andincluding a fusible element extending axially through said fuse tube, aninsulating tube of gas evolving material within said fuse tubesurrounding said fusible element, a conductive sleeve within said fusetube circumjacent said insulating tube along the entire length of saidfusible element and having an external diameter substantially smallerthan the inner diameter of said fuse tube, said fusible element, saidinsulating tube, and said conductive sleeve being stationarily mountedrelative to said fuse tube, said insulating tube being rupturable bycurrent flowing through said fuse link and said conductive sleevestructurally reinforcing the insulating tube and thereby increasing themagnitude of current that can be interrupted in said insulating tubewithout rupture thereof, one end of said insulating tube extendingbeyond said sleeve and higher magnitudes of current flowing through saidfuse link rupturing said insulating tube, the gases evolved from saidexpulsion fuse tube as a result of the are formed by said highermagnitudes of current extinguishing said arc, said conductive sleeveserving as a terminus for said are and reducing the length of the arewithin said fuse tube, whereby the internal pressure within said fusetube is decreased.

3. in a fuse cutout of the expulsion type, in combination, a gasevolving expulsion fuse tube, a fuse link including a fusible elementextending axially through said fuse tube, an insulating tube of gasevolving material within said fuse tube in surrounding relation to saidfusible element, and a conductive sleeve within said fuse tube closelycircurnjacent said insulating tube along the entire length of saidfusible element and having an external diameter substantially smallerthan the internal diameter of said fuse tube, said insulating tube beingrupturable as a result of current flow through said fuse link and oneend of said insulating tube extending beyond said conductive sleeve andsaid conductive sleeve structurally reinforcing said insulating tube andthereby increasing the magnitude of current that can be extinguished insaid insulating tube Without rupture thereof, said fuse link, saidinsulating tube, and said conductive sleeve being stationarily mountedrelative to said fuse tube, high magnitudes of current flowing throughsaid fuse link rupturing said insulating tube and the gases evolved fromsaid expulsion fuse tube as a result of the are formed by said highmagnitudes of current extinguishing said arc, said sleeve serving as aterminus for said are and reducing the length of the are within saidfuse tube, whereby the internal pressure within said fuse tube isdecreased.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN A FUSE CUTOUT OF THE EXPULSION TYPE, IN COMBINATION, A GASEVOLVING EXPULSION FUSE TUBE, UPPER AND LOWER METALLIC CONTACTS ADJACENTTHE ENDS OF SAID FUSE TUBE, A FUSE LINK INCLUDING A FUSIBLE ELEMENTEXTENDING AXIALLY THROUGH SAID FUSE TUBE, SAID FUSE LINK INCLUDING ABUTTON HEAD ELECTRICALLY CONNECTED TO SAID UPPER CONTACT AND A DEPENDINGCYLINDRICAL SHANK AND BEING CONNECTED ADJACENT ITS LOWER END TO SAIDLOWER CONTACT, AN INSULATING TUBE OF GAS EVOLVING MATERIAL SURROUNDINGSAID FUSIBLE ELEMENT AND SAID DEPENDING SHANK WITHIN SAID FUSE TUBE, ACONDUCTIVE SLEEVE WITHIN SAID FUSE TUBE CLOSELY ADJACENT SAID INSULATINGTUBE ALONG THE ENTIRE LENGTH OF SAID FUSIBLE ELEMENT AND HAVING ANEXTERNAL DIAMETER SUBSTANTIALLY SMALLER THAN THE INNER DIAMETER OF SAIDFUSE TUBE, SAID FUSE LINK, SAID INSULATING TUBE, AND SAID CONDUCTIVESLEEVE BEING STATIONARILY MOUNTED RELATIVE TO SAID FUSE TUBE, SAIDINSULATING TUBE BEING RUPTURABLE AS A RESULT OF CURRENT FLOW THROUGHSAID FUSE LINK AND SAID CONDUCTIVE SLEEVE STRUCTURALLY REINFORCING SAIDINSULATING TUBE AND THEREBY INCREASING THE MAGNITUDE OF CURRENT THAT CANBE EXTINGUISHED IN SAID INSULATING TUBE WITHOUT RUPTURE THEREOF, THELOWER END OF SAID INSULATING TUBE EXTENDING BEYOND SAID SLEEVE AND HIGHMAGNITUDES OF CURRENT FLOWING THROUGH SAID FUSE LINK RUPTURING SAIDINSULATING TUBE, THE GASES EVOLVED FROM SAID EXPULSION FUSE TUBE AS THERESULT OF THE ARC FORMED BY SAID HIGHER MAGNITUDES OF CURRENTEXTINGUISHING SAID ARC, SAID CONDUCTIVE SLEEVE SERVING AS THE TERMINUSFOR SAID ARC AND REDUCING THE LENGTH OF THE ARC WITHIN SAID FUSE TUBE,WHEREBY THE INTERNAL PRESSURE WITHIN SAID FUSE TUBE IS DECREASED.